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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #1  
Old 19th August 2014, 09:29
wasz wasz is offline
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Default Marlin Cabrio compression strut conversion

We have a pinto powered Marlin cabrio that hops over bumps in the road at the front and front suspension feels very stiff.

It runs AVO V 974 adjustable coilovers and I've calculated the the springs to be 145lb/ft each which seems to be in spec.

However it is running the massive anti roll bar setup from the Sierra and I suspect it is that causing the front end to hop about.

I understand from elsewhere that Sierras had a number of different size ARBs and some people fit the smaller 24mm one from the P100 which might go someway to resolving the issue. I will try and find one of those....

However I've also heard of "compression struts" designed for the Sierra to do away with the roll bar completely for fully independent suspension (since the cabrio is so light, does it need a roll bar?).

If I wanted to fit these to the cabrio, they they just bolt up to the ARB mounting points? Is anything else needed?

Can I just buy these and bolt them on?

http://www.burtonpower.com/parts-by-...rra-mp593.html

I saw on the owners club forum some people had to cut them down by 10mm. Is that all that would be required?

Anyone got experience?

Thanks!
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  #2  
Old 19th August 2014, 10:02
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cabrioman cabrioman is offline
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The sierra compression struts bolt straight on, some depending on make may need to be cut down.

The only thing to watch out for is there are two PCD spacings for the chassis mounting brackets, one for standard Sierra and one for the 4x4 Cosworth. I think from memory they are 90mm and 95mm respectively.

You may want to consider buying the struts from Compbrake in conjunction with their adjustable TCA's. They sometimes do some good bundle deals from time to time. The adjustable arms make a massive difference to the adjustment of the front Camber.

Adjustment using the daft standard shimming method is almost impossible on the Cabrio with the wings in place and quite often the studs fitted by Marlin were too short to allow the required number of shims.

John
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Old 19th August 2014, 11:01
wasz wasz is offline
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Hi cabrioman - thanks for the reply!

Do you have them fitted to your car - do they stop the front end skipping about?

Are the compbrake ones the best brand to go for / do you know which ones will fit without any shortening?

Interesting you mention the TCAs - we've never had to adjust the camber on this car, but will have to have it checked out after fitting these. Are there some recommended settings?

Last edited by wasz; 19th August 2014 at 11:05..
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Old 19th August 2014, 21:24
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cabrioman cabrioman is offline
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They were fitted to mine to allow fitment of the Bmw straight 6, which will not really fit with an anti roll bar.

I suspect your skipping problem is more likely to be a combination of too heavy arb (the 24mm is the best), tyre pressures and steering geometry.

The advantage of compression struts and adjustable track control arms is that you can then set up the front end steering and suspension geometry precisely and easily at a professional 4 wheel laser tracking outfit, which would not be possible with an arb and messing around with shims on the tca mounts.

Compbrake are well thought of but will need minor mods on the strut length, which is straight forward to do. If you have a look on the moc site forum cosworthlee fitted compbrake struts and tca's, there are pictures on the listing.

I think most folks have gone with about 1 degree of camber with 4 degree of caster.

John
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Old 20th August 2014, 14:14
Mike Mike is offline
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Hi Will

I bought my TCAs from Compbrake, as the quality is good and their prices are the best. They were very easy to fit, and as John says, make setting the Camber so much easier.
Compression struts would then make setting Castor just as easy. Again as John says trying to set the wheel geometry up using top link shims as Marlin suggest is not easy at all. Each shim fitted changes both Castor and camber, so there is quite a lot of trial and error to get to the desired Castor and Camber at the same time. With adjustable TCAs and Compression struts this would be so much easier, allowing it to be done at a professional Wheel Alignment outfit.

It is also important to set up the rear suspension geometry, as many Cabrios appear to have an in-built Marlin manufacturing alignment fault.

Toe-in is often excessive on one of the rear wheels.

The solution is to fit shims between the rear hub carrier and the trailing radius arm. It is again trial and error, but worth the effort.

Peter Licence posted some good advice on the MOC


Mike
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Old 15th September 2014, 20:41
wasz wasz is offline
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Hi thanks everyone!

Finally got near the cabrio again at the weekend. Turns out it has a 24mm ARB after all (duh).

We had the front AVO coil over units off last time (leaky and seized adjusters) and sent for a refurb. I asked to make them 20% softer and they did.

We fitted them up (on the softest setting, and the coils with 5mm less preload than before) and the car passed the MOT style bounce test.

Hit the road and the car is transformed! Much better - who knows what they were set to previously! We are thinking to leave it at that for a bit and shelve the TCA idea for the time being.

Its running 150lb/ft springs which are softer than I've heard are usually fitted to cabrios.

Probably not the ideal setup - to my engineering mind TCAs would be better as the ARB was for a heavier car, but if we fit TCAs we may end up needing heavier springs. Its a road car so we aren't chasing the ultimate nuances in handling.

We did hit another problem, looks like fuel is not coming through properly (I think its a blockage between tank and pump) so we had to tow it home!

Thanks for the advice on the rear toe, will probably investigate this over winter.

Last edited by wasz; 15th September 2014 at 21:37..
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